1. Field of the Invention
The present invention relates to a method of determining a reflective surface of a reflector in a vehicle lamp used in vehicles such as automobiles and the like.
2. Related Background Art
The vehicle lamps need to meet (1) the conditions from the aspect concerning the function as lamps and, in addition thereto, (2) the conditions from the aspect concerning the shape (shape constraints), and (3) the conditions from the aspect concerning the appearance (appearance constraints) because of their use in a mounted state on the vehicles such as the automobiles and the like. It is thus necessary to realize lamps optimized as to the conditions from the functional aspect while satisfying the given constraints from the shape aspect and the appearance aspect.
The conditions from the functional aspect include light uniformity with which the entire lamp lights uniformly, light diffusibility with which light is properly diffused to be observed from various directions, and so on, depending upon types of lamps.
As for the constraints from the vehicle and body side, the shape constraints include conditions defined by the volume and shape of lamp receiving portions of the body, the continuous shape of the outer surface of the lamp (the outer surface of lens) from the other body portions, and so on. The appearance constraints include conditions resulting from harmony with the appearance of the other body portions, requirements from the design aspect of the body, and so on.
In recent years, there are increasing needs for lamps meeting strict shape constraints, e.g., further decrease in the depth of the lamp, because of restrictions on the lamp receiving portions from the aspect of construction of the body, the increasing tendency toward fascinating styling of cars, and so on. Under such circumstances, when a lamp was constructed, for example, using a reflector wherein the basic shape of its reflective surface was a unifocal paraboloid, decrease was insufficient in the thickness of the lamp and it was difficult to comply with the above-stated shape constraints such as the decrease in the depth of the lamp.
As against it, another reflector was proposed in such structure that the basic shape of the reflective surface was a free-formed surface created so as to match the shape constraints and other conditions. With use of the free-formed surface, it is relatively easy to meet the shape constraints such as the decrease in the depth of the lamp because of its degrees of freedom in designing thereof (for example, reference is made to Japanese Patent Application Laid-Open No. H09-33708). However, since reflective surface shapes of respective portions in the reflective surface need to satisfy the conditions from the functional aspect of reflecting the light from a light source into the direction along the given optical axis, they are normally formed in the shape of paraboloid of revolution or in the shape approximate thereto with light diffusing capability. Therefore, the reflective surface is formed by dividing the above-stated free-formed surface into a plurality of segments and assigning reflective surface elements having respective, reflective surface shapes of paraboloids of revolution or the like to the respective segments.
When the shape of the entire reflective surface is determined by first determining the free-formed surface as a basic shape, thereafter dividing the free-formed surface into segments, and then assigning reflective surface elements to the segments as described above, there can occur nonuniformity of in-surface reflection distribution of the light from the light source; e.g., on the reflective surface in each reflective surface element there appears a dark area even during on periods of the lamp as it is shadowed by another reflective surface element in a view from the light source. The optical nonuniformity would be unobtrusive during the on periods of the lamp as long as such dark areas appear at relatively low rates and at approximately uniform rates in the respective reflective surface elements.
In the creation of the reflective surface using the free-formed surface as a basic shape, however, the shape thereof normally largely varies among individual lamps, depending upon the given shape constraints and other conditions, and the shape of the free-formed surface often becomes asymmetric. Particularly, the conditions for the decrease in the depth of the lamp impart severe conditions on incidence of the light from the light source and on reflection thereof into the direction of the optical axis at each part of the reflective surface. For that reason, there arise problems that it becomes difficult to obtain the reflective surface with unobtrusive distribution nonuniformity of bright portions receiving and reflecting the light and the other dark portions while satisfying the given shape constraints in each lamp and that the design efficiency is lowered, e.g., because the shape of the reflective surface has to be redesigned many times in the design steps.
The present invention has been accomplished in view of the above problems and an object of the present invention is to provide a method of determining a reflective surface of a reflector in a vehicle lamp, by which the reflective surface consisting of a plurality of reflective surface elements can be determined with reduced in-surface distribution nonuniformity of light during the on periods of the lamp and at increased design efficiency.
In order to accomplish the above object, a reflective surface determining method of a reflector in a vehicle lamp according to the present invention is a method comprising (1) a condition setting step of setting a light source position at which a light source is to be placed, and an optical axis that passes the light source position and that defines a direction into which light from the light source is to be reflected by a reflector; (2) a free-formed surface creating step of creating a free-formed surface satisfying a predetermined shape constraint; (3) a free-formed surface selecting step of selecting the free-formed surface satisfying a predetermined functional condition, as a free-formed surface to be used for creation of a reflective surface; (4) a reflective surface creating step of dividing the free-formed surface selected, into a plurality of segments and assigning a reflective surface element for reflecting the light from the light source placed at the light source position, into the direction along the optical axis, to each of the segments, thereby creating a reflective surface including a plurality of reflective surface elements; and (5) a reflective surface selecting step of setting an evaluation axis for evaluation of optical reflection characteristics of the reflective surface, preparing a light reflecting region distribution by determining for each portion of the reflective surface a reflecting region accepting the light from the light source placed at the light source position and reflecting the light into a direction of the evaluation axis, and selecting the reflective surface with the light reflecting region distribution satisfying a predetermined region distribution condition, as a reflective surface to be used for the reflector.
In the above reflective surface determining method of the reflector in the vehicle lamp, as to the shape of the reflective surface obtained in the determination (or in the designing) of the reflective surface, the evaluation and selection during the designing thereof is carried out at each of the two stages, which are the stage of creation of the free-formed surface being the basic shape and the stage of creation of the reflective surface with the plurality of reflective surface elements assigned. This provides the reflective surface determining method capable of efficiently obtaining the reflector of the vehicle lamp that satisfies the shape constraints including the decrease in the depth and that realizes the preferred optical uniformity during the on periods in terms of the function of the lamp.
In this method, the evaluation and selection at the stage of the free-formed surface is carried out according to the condition from the functional aspect as a reflective surface of the reflector used in the lamp (functional condition). At the stage of the creation of the free-formed surface, some consideration can be given to the condition of optical uniformity and other conditions as a reflective surface. The shape of this free-formed surface also affects the way of making a shadow after the creation of the reflective surface elements. The evaluation on these problems is conducted at the stage of the free-formed surface and then the selection of the free-formed surface is performed.
The evaluation and selection at the stage of the reflective surface consisting of the plurality of reflective surface elements is carried out according to the reflecting regions that reflect the light into the direction of the set evaluation axis. A light reflecting region on the reflective surface indicates how the region is seen (or how the region is lighting) when the lamp is seen from the direction of the evaluation axis during the on periods of the lamp. In this respect, there arise the problems including the problem that the dark area appears even during the on periods of the lamp while being shadowed by another reflective surface element in a view from the light source, on the reflective surface in each reflective surface element, as described above. At the stage of the reflective surface, the evaluation on these problems is conducted with preparation of the light reflecting region distribution and then the selection of the reflective surface is carried out.
The occurrence of nonuniformity can be reduced in the in-surface light distribution during the on periods of the lamp on the finally obtained reflective surface by carrying out the evaluation and selection by the different methods at the two stages as described above, different from the method in which the evaluation of the reflective surface shape is carried out, for example, only at the stage of the reflective surface consisting of the plurality of reflective surface elements. The design efficiency can be improved by simplifying the design steps for obtaining the reflective surface with preferred optical uniformity.
The evaluation of the reflective surface in the reflective surface selecting step can be performed, for example, by checking how each portion in the reflective surface lights up during the on periods of the lamp by a method of ray tracing or the like based on computation.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.